M cells in the epithelium over lymphoid follicles transport bacteria, viruses and antigenic macromolecules from the intestinal lumen into Peyer's patches where immune responses are initiated. The aim of the proposed research is to identify cell surface molecules specific to M cells which may be relevant to differentiation and functional competence. Enzymatic dissocation procedures will be used to differentially remove epithelium over lymphoid follicle surfaces. Isolated cell populations will be examined for ultrastructural, cytochemical and functional properties characteristic of M cells. Enriched populations of follicle epithelial cells will be obtained by employing cell separation methods. Cell sorting will be used to separate M cells from isolated Peyer's patch epithelial populations after phagocytosis of fluorescent latex microspheres. Enriched populations of M cells will be used to generate monoclonal antibodies through somatic cell hybridization and as screening tools to assess the reactivity of the antibodies. The specficity of monoclonal antibodies directed to M cell surface antigens will be examined directly in Peyer's patch tissue. The production of M cell specific antibodies will allow us to separate M cells from heterogeneous mixtures of Peyer's patch lymphoepithelial cells, to study the ontogeny and functional significance of M cell surface molecules and to investigate functional interactions between M cells and cells of the mucosal immune system.